I haven’t touched the terrain tool in Unity3D since 2.5, which is a reference more to the time that’s passed than the improvements in the terrain engine, which have been minimal.
While refamiliarizing myself with the base textures and splatmaps, I ran into some great work by Larsbertram‘s work on changing the shaders on the terrain map so they look seamless, and he created the free set of terrain shaders downloadable at the Asset Store here: Advanced Terrain Shaders V2
The technique to reduce texture tiling involves mixing the shader with a copy of itself at a scale of 4x (which you can play with in different textures for best result) which looks good from far away and close up. His article on this technique is in a post called Improved Texture Terrain Tiling and is very much worth a read.
He heavily references an amazing article called Terrain Advanced Textures which goes much more in depth into the technique. This article is geared towards Unreal Engine, but the underlying concepts will help to make textures look more natural and less tiled in almost any 3D program. It shows in depth techniques how to design the materials, as well as scaling, tiling and mapping them for ultimate effectiveness.
This technique can help you go from this to that: